The present invention relates to a system and method for controlling fuel injection, and more particularly, to a system and method for controlling fuel injection, in which a MAP (manifold absolute pressure) sensor is used to calculate variations in intake pressure in a purge interval to control the amount of fuel that is injected.
An ECU (electronic control unit) is typically provided in an engine to perform overall control of the engine. For example, the ECU receives various inputs such as vehicle speed, engine rpm, etc., and controls a fuel injector based on the received data.
Since the majority of air pollution caused by vehicles is a result not only of exhaust gases but of fuel vapors, measurements are taken in most vehicles to minimize the escape of fuel vapors into the atmosphere. In particular, hydrocarbons evaporated from the fuel tank are stored in a canister and then supplied at suitable times to the engine through a purge control solenoid valve (PCSV). Accordingly, the amount of fuel vapors released into the atmosphere is greatly reduced. For ease of explanation, evaporated hydrocarbons in the canister will be referred to as xe2x80x9cpurge fuelxe2x80x9d. Similarly, fuel injected from the canister will be referred to as fuel xe2x80x9cpurgedxe2x80x9d from the canister.
The amount of fuel purged to the engine through the PCSV directly influences engine operation, thereby controlling the amount of purge fuel supplied to the engine. If an excessive amount of fuel vapors or pure air is purged to the engine at idle speed, the air-fuel mixture becomes too rich or lean, respectively, which may result in stalling of the engine.
To remedy this problem, when the purge fuel is supplied to the engine, purge fuel feedback control is performed such that if the concentration of hydrocarbons in the purge fuel is high, a purge fuel feedback value is increased, and the amount of fuel injected into the engine through the fuel injector is decreased by the feedback value.
FIG. 3 shows a block diagram of a conventional system to control fuel injection. In the conventional system, an ECU 51 receives signals from a PCSV 53, an engine rpm sensor 55, a throttle position sensor 57, an oxygen sensor 59, and a coolant temperature sensor 61, and then controls a fuel injector 63 according to the received signals.
FIG. 4 shows a flow chart of a method for controlling fuel injection using the above system.
The ECU 51 receives a purge duty signal from the PCSV 53 to detect a purge interval in step S100. That is, a signal value greater than 0 when a coolant temperature is greater than or equal to a predetermined value, and basic fuel feedback conditions are not satisfied indicating that fuel is not being purged.
If conditions for a purge interval are satisfied in step S100, it is determined whether fuel feedback control is being performed in step S110. That is, fuel feedback control is performed if the oxygen sensor 59 is activated and the coolant temperature is greater than or equal to a predetermined value, and in fuel feedback control, feedback gains including an integral gain (I-gain) and a proportional gain (P-gain), are measured. The feedback gains establish an acceleration fuel injection quantity determined to be suitable during acceleration when there is a change from a throttle-off state (i.e., when a throttle valve is closed) to a throttle-on state (i.e., when the throttle valve is open), after which the fuel injection amount is supplied to the engine through the fuel injector 63. The feedback gains are also implemented during acceleration such that harmful elements in the exhaust gases are reduced.
If it is determined that fuel feedback control is being performed in step S110, the ECU 51 calculates a purge ratio Pr and a purge concentration Pc in step S120. The purge ratio Pr is a ratio of purge air to intake air (purge air/intake air), while the purge concentration Pc is a ratio of a purge fuel amount to a purge amount (purge fuel amount/purge amount). The following are equations for calculating the purge ratio Pr and the purge concentration Pc.                               A          /          F                =                                                                                                  (                                          amount                      ⁢                                              xe2x80x83                                            ⁢                      of                      ⁢                                              xe2x80x83                                            ⁢                      intake                      ⁢                                              xe2x80x83                                            ⁢                      air                      xc3x97                      air                      ⁢                                              xe2x80x83                                            ⁢                      density                                        )                                    +                                                                                                      (                                      amount                    ⁢                                          xe2x80x83                                        ⁢                    of                    ⁢                                          xe2x80x83                                        ⁢                    purge                    ⁢                                          xe2x80x83                                        ⁢                    air                    xc3x97                    air                    ⁢                                          xe2x80x83                                        ⁢                    density                                    )                                                                                                                                              (                                          base                      ⁢                                              xe2x80x83                                            ⁢                      fuel                      ⁢                                              xe2x80x83                                            ⁢                      amount                      xc3x97                      liquid                      ⁢                                              xe2x80x83                                            ⁢                      fuel                      ⁢                                              xe2x80x83                                            ⁢                      density                                        )                                    +                                                                                                      (                                      purge                    ⁢                                          xe2x80x83                                        ⁢                    fuel                    ⁢                                          xe2x80x83                                        ⁢                    amount                    xc3x97                    gaseous                    ⁢                                          xe2x80x83                                        ⁢                    fuel                    ⁢                                          xe2x80x83                                        ⁢                    density                                    )                                                                                        [                  Equation          ⁢                      xe2x80x83                    ⁢          1                ]            
If feedback control is performed, an average A/F (air/fuel ratio) is maintained at the stoichiometric value 14.7. Equation 1 is used for Equation 2 below.                     Pc        =                                                                              1                  +                  Pr                  -                                                                                                      (                                      I                    -                                          gain                      xc3x97                      purge                      ⁢                                              xe2x80x83                                            ⁢                      fuel                      ⁢                                              xe2x80x83                                            ⁢                      amount                      ⁢                                              xe2x80x83                                            ⁢                      compensation                      ⁢                                              xe2x80x83                                            ⁢                      value                                                        )                                                                          Pr            xc3x97                          (                              1                +                                  14.7                  xc3x97                                                            gaseous                      ⁢                                              xe2x80x83                                            ⁢                      fuel                      ⁢                                              xe2x80x83                                            ⁢                      density                                                              air                      ⁢                                              xe2x80x83                                            ⁢                      density                                                                                  )                                                          [                  Equation          ⁢                      xe2x80x83                    ⁢          2                ]            
Here, I-gain is assumed to be 1.0, the gaseous fuel density is assumed to be 3.21 g/l, and the air density is assumed to be 1.29 g/l. Consequently, Equation 2 becomes as follows:                     Pc        =                              1            +            Pr            -                          purge              ⁢                              xe2x80x83                            ⁢              fuel              ⁢                              xe2x80x83                            ⁢              amount              ⁢                              xe2x80x83                            ⁢              compensation              ⁢                              xe2x80x83                            ⁢              value                                            37.6            xc3x97            Pr                                              [                  Equation          ⁢                      xe2x80x83                    ⁢          3                ]            
After the calculation of the purge ratio Pr and the purge concentration Pc in step S120, a purge fuel amount compensation value (% fuel_purge) is calculated using the purge ratio Pr and the purge concentration Pc values in step S130. The purge fuel amount compensation value (% fuel_purge) is calculated using Equation 4 below.
% fuel_purge=1+Prxe2x88x9237.6xc3x97Prxc3x97Pcxe2x80x83xe2x80x83[Equation 4]
Subsequently, a final fuel amount (% fuel_final) for supply to the fuel injector 63 is calculated in step S140. The final fuel amount (% fuel_final) is calculated using Equation 5 below.
% fuel_final=base fuel amountxc3x97(1xe2x88x92% fuel_purge)xe2x80x83xe2x80x83[Equation 5]
However, with the control of fuel injection using the above method, in a high temperature state or in an idle state, for example, where a fuel of a high volatility is used and/or if the vehicle is left idling for long periods, a large amount of purge gas (mostly hydrocarbons) accumulates in the canister. If the vehicle is then driven in this state, a significant amount of purge gas is supplied to the engine through the PCSV. At this time, the purge fuel amount compensation value (% fuel_purge) increases such that the final fuel amount (% fuel_final) supplied through the fuel injector 63 decreases. This result is evident from Equation 5.
If the vehicle is driven from an idle state under such conditions, (a) a difference between an intake pressure during idle and an intake pressure in a part load state causes a difference in pressure variation values between opposing ends of the PCSV 53, (b) a calculated amount (a desired amount) of purge fuel is not supplied to the engine, and (c) the final fuel amount (% fuel_final) is decreased such that the engine air to fuel ratio (A/F) becomes lean and the driver experiences hesitation or a jerky forward motion.
Further, in a low temperature state or when a fuel of a low volatility is used, since there are almost no fuel vapors in the fuel tank, hydrocarbons do not accumulate in the canister. Accordingly, during the supply of purge gas to the engine, it is mostly air that is being supplied. If feedback is performed under such conditions, a negative value results for the purge fuel amount such that the final fuel amount (% fuel_final) increases. At this time, if the vehicle is operated in an idle state, a difference in pressure variation values between opposing ends of the PCSV 53 results, and the amount of purge fuel supplied to the engine is greater than that calculated (desired) such that a rich air to fuel ratio results, thereby causing the combustion of unneeded fuel.
The present invention provides a system and method for controlling fuel injection, in which a MAP (manifold absolute pressure) sensor is used to calculate variations in intake pressure in a purge interval to compensate a final fuel amount supplied to the engine, thereby improving drive performance and minimizing fuel consumption.
The present invention thus provides a method for controlling fuel injection, in which an ECU for controlling an engine calculates a base fuel amount, receives an output voltage from an oxygen sensor, and calculates a purge fuel amount compensation value and a final fuel amount using a feedback gain, a purge ratio, and a purge concentration, which are based on a difference between the output voltage and a standard voltage, after which the ECU controls a fuel amount that is supplied through a fuel injector. The method of the invention thus includes detecting a purge duty signal and determining if conditions for a purge interval of the engine are satisfied; determining if conditions for feedback control of the engine are satisfied; receiving intake pressure signals from a MAP sensor; calculating the purge ratio and the purge concentration; calculating the purge fuel amount compensation value using the purge ratio and the purge concentration; determining if the purge fuel amount compensation value is greater than a first critical rate; calculating a change in intake pressure if the purge fuel amount compensation value is greater than the first critical rate; determining if the change in intake pressure is greater than a first critical value; calculating a first final fuel amount compensation value if the change in intake pressure is greater than the first critical value, and controlling the final fuel amount using the first final fuel amount compensation value; determining if the purge fuel amount compensation value is less than a second critical rate if the purge fuel amount compensation value is not greater than the first critical rate; calculating the change in intake pressure if the purge fuel amount compensation value is less than the second critical rate; determining if the change in intake pressure is less than a second critical value; and calculating a second final fuel amount compensation value if the change in intake pressure is less than the second critical value, and controlling the final fuel amount using the second final fuel amount compensation value.
The change in intake pressure is preferably obtained by taking the absolute value of a difference between a present intake pressure and a previous intake pressure.
The first final fuel amount compensation value is obtained by subtracting a product of a compensation constant, the change in intake pressure, and the purge fuel amount compensation value from the integer 1, then multiplying the result by the base fuel amount.
The second final fuel amount compensation value is obtained by subtracting a product of a compensation constant, the change in intake pressure, and the purge fuel amount compensation value from the integer 1, then multiplying the result by the base amount.
The present invention also provides a system for controlling fuel injection comprising an ECU for controlling an engine including a fuel injector of the engine according to signals received from a purge control solenoid valve, an engine rpm sensor, a throttle valve position sensor, an oxygen sensor, and a MAP sensor for indirectly detecting an intake pressure from vacuum variations of an intake manifold and output voltage signals. The ECU, in a purge interval, calculates a base fuel amount and a purge fuel amount compensation value, and when changing from one of an idle state and a light load state to one of a part load and a full load state, applies a first final fuel amount compensation value to compensate a final fuel amount in the case where the purge fuel amount compensation value is excessively positively learned. The first final fuel amount compensation value is obtained by subtracting a product of a first compensation constant, a change in intake pressure, and the purge fuel amount compensation value from the integer 1, then multiplying the result by the base fuel amount. The ECU, when changing from one of the part load state and the full load state to one of the idle state and the light load state, applies a second final fuel amount compensation value to compensate the final fuel amount in the case where the purge fuel amount compensation value is determined to be excessively negative. The first final fuel amount compensation value is obtained by subtracting a product of a second compensation constant, a change in intake pressure, and the purge fuel amount compensation value from the integer 1, then multiplying the result by the base fuel amount.
According to a further alternative embodiment of the invention, the electronic control unit is programed to execute instructions for controlling an amount of fuel to a fuel injector based on parameters comprising at least a change in intake pressure as calculated by the ECU based on signals received from a MAP sensor. The control is preferably based on additional parameters, for example feedback gain, purge ratio, purge concentration and selected critical rates. In a further preferred embodiment, the ECU is programed to calculate a base fuel amount and a purge fuel amount compensation value by which the base fuel amount is multiplied to determine a final fuel amount. The purge fuel amount compensation value is preferably based at least in part on said change in intake pressure.